New insight into microgel-stabilized emulsions using transmission X-ray microscopy: nonuniform deformation and arrangement of microgels at liquid interfaces.

Microgel-covered interfaces, e.g., in emulsions, have attracted much interest lately. Different imaging techniques have been used to image these interfaces, either flat or curved, to investigate their properties and appearance. Techniques such as cryogenic scanning electron microscopy (cryo-SEM) and confocal microscopy have provided valuable insight into microgel-covered systems but still have some disadvantages such as part of the microgels being trapped in vitrified liquid or the need for fluorescent markers. Some of these disadvantages can be overcome by using transmission X-ray microscopy (TXM), which has the advantage of allowing the investigation of adsorbed and free microgels simultaneously. We used TXM to acquire tomographic image series of microgel-covered droplets and calculated 3D reconstructions from these image stacks. As a result, we could show that microgels deform anisotropically and penetrate the oil droplets in the hydrated state. Additionally, 3D reconstruction gives an idea of the arrangement of microgels adsorbed to oil droplets and reveals that droplet stabilization is possible without full coverage of the interface with polymer segments.